Nitrogen triiodide is a contact explosive, meaning it explodes at the slightest touch. The unstable substance will blow up even if something as light as a mosquito or a helium balloon comes in contact with it. 

In the video above, the folks at the Royal Institution, a British nonprofit for scientific education, explain why nitrogen triiodide explodes at the smallest touch, releasing a dark cloud of purple gas. It has to do with where the iodine molecules bond to the nitrogen atom, a chemical fact best explained with balloons. 

Come for the nerdy science explanations, stay for the slow-mo explosions. 

[h/t: Digg]